This invention relates to glasses having low transmission in the infrared range, and in particular to aluminophosphate glasses containing copper(II) oxide.
Such glasses are used, e.g., as color correction filters in color video cameras, as shields for illuminated color displays (e.g., in aircraft cockpits), as stray light filters in monochromators, as graduated filters, as an inorganic component in plastic composite filters or as goggles.
The glasses should have as high a transparency as possible in the near UV range and in the visible range of light (about 400-625 nm) and as low as possible a transparency in the infrared range (above about 625 nm). In this case, the glass is largely color-neutral. The weathering resistance must be sufficient to ensure that the spectral transmission characteristic remains unchanged in humid air. A low thermal expansion is also necessary, especially for the industrial production of large-surface filters.
A large number of such glasses have already been described. In DE 29 08 697 B2, a glass with a high barium content is described, but in which the Al.sub.2 O.sub.3 content has to be kept low, which thereby has a negative effect on the weathering resistance. DE 32 29 442 Al describes a phosphate glass on the basis of P.sub.2 O.sub.5 /Sb.sub.2 O.sub.3 /alkaline-earth oxygen+zinc oxide. The high content of Sb.sub.2 O.sub.3 and alkaline-earth oxides has the disadvantage that, caused by the high index of refraction of these glasses, sizable light losses due to scattering must be accepted in areas where the filters meet. Moreover the weathering resistance is drastically reduced by the alkaline-earth metal oxides SrO and BaO.
JP-PS 59 15 102, JP-OS 60 23 57 40 and JP-PS 61 59 256 also describe glasses having high contents of alkaline-earth metal oxides (+ZnO). In the first two mentioned Japanese patents, the B.sub.2 O.sub.3 portion is relatively low, which leads to an increased transformation temperature (Tg). Such glasses having a great viscosity change in a narrow temperature range can be produced only with difficulty.
JP-OS 62 15 3144 and JP-OS 62 12 89 43 describe glasses free of alkali metal, which are not easy to melt. Finally, JP-OS 57 149 845 and JP-OS 63 25 245 describe phosphate glasses, which contain a content of Fe.sub.2 O.sub.3 or SnO.sub.2.
Although, as is evident, numerous CuO-containing phosphate glasses already exist, there is still a demand for improved glasses.